1. Field of the Invention
The present invention relates to a display apparatus for providing pictures by scanning light emitted from a light source.
2. Description of the Prior Art
As displays, flat-panel picture display apparatuses such as liquid crystal displays and CRT displays are generally known. As a display apparatus capable of inexpensively providing high-definition pictures, a scanning picture display apparatus has been disclosed.
The scanning picture display apparatus is designed to display pictures to the viewer's eye by scanning light emitted from a light source. For example, Japanese Laid-open Patent Applications Nos. H4-100088 and H7-135623 disclose picture display apparatuses of this type. These apparatuses provide two-dimensional pictures by scanning in the horizontal and vertical directions light emitted from a point light source.
In order for a scanning picture display apparatus to provide stable pictures, it is a condition to perform stable light scanning. Vibration of a mirror is typically used as light scanning means. These apparatuses include means for controlling the amplitude and the speed of the vibration mirror so that stable light scanning is performed. In the conventional apparatuses, means for detecting the movement of the vibration mirror is provided and based on the result of the detection, the controlling means controls the vibration mirror.
FIG. 1 schematically shows the structure of an example of a scanning mirror having the detecting means. Reference numeral 32 represents the scanning mirror and reference numerals 31 and 33 represent the detecting means. Of these detecting means, the detecting means 31 is a light intercepting plate and the detecting means 33 is a photointerruptor. The scanning mirror 32 is held by a mirror holder 34 and vibrates by being driven by driving portion 35. The light intercepting plate 31 operates in conjunction with the vibration of the scanning mirror 32.
By the light intercepting plate 31 moving, a space 33a serving as the optical path of photoelectrons of the photointerruptor 33 is intercepted or not intercepted. Therefore, by detecting the voltage, the movement of the light intercepting plate 31 is determined, so that the movement of the scanning mirror 32 is detected. Based on the result of the detection, the controlling means controls driving portion 35 for driving the scanning mirror 32.
In the scanning picture display apparatus, since pictures are provided to the viewer's eye by scanning light from a point light source, light having a higher intensity than the light provided by a flat-panel picture display apparatus is required to provide sufficiently bright pictures. However, when high-intensity light is emitted from a point light source, if scanning is stopped because of a failure in scanning means, high-intensity light will concentrate on one point on the viewer's eye, which can cause troubles to the viewer's eye. Therefore, in the conventional apparatus, it is impossible to emit light having sufficiently high intensity for making the provided pictures sufficiently bright for the viewer.
In order to detect the movement of the vibration mirror, the detecting means is provided on the vibration mirror. In this arrangement, the detecting means can impair the vibration of the mirror. In order to provide high-definition scanning pictures, it is necessary for the vibration frequency of the mirror to be high. However, the weight of the detecting means provided on the mirror limits the frequency.